The first gives any attack a chance at creating a corpse, the second gives you essence when you explode one, the third gives a damage bonus for exploding a corpse, and the last gives you Fortify whenever a corpse is created, which is great for early game survivability. The most important passives for this build are Hewed Flesh, Grim Harvest, Fueled by Death, and Necrotic Carapace. You'll also need to unlock a basic skill, so I recommend Decompose, which serves as a great way to create corpses and generate essence in the early game, before you unlock reapers, as well as essence and corpse generating passives.

Bone Storm: This ultimate provides great survivability for the Necro, especially once you get the Aspect of the Shielding Storm that allows it to create a barrier.

Raise Dead: Your classic way to re-recruit fallen minions.

Iron Golem Slam: This is your Iron Golem's core ability that stuns enemies in an AoE and makes them vulnerable.Plagued Corpse Tendrils: This ability slows, stuns, and makes enemies vulnerable, plus groups them up for more effective explosion damage.Plagued Corpse Explosion: A key component of this build this ability deals a stacking damage bonus to stunned, slowed, and vulnerable enemies, but can also generate essence with the Grim Harvest passive.It can also be made better with the Splintering Aspect and the Unique Deathless Visage helm in the late game. Bone Spear: This core skill is a good investment, letting you apply vulnerable at will for better explosion damage.

Skeleton necromancer build diablo 2